this, all day long
One piece of advice though. Aside from all the technical crap re: audio specs etc, watch out for how you interact with the unit.
The big thing now that's becoming common is fancy touch screen displays where the whole the unit face is just a touch screen. Don't fall into that trap.
This is neat and sexy and lets the mfr make all kinds of super flexible display options, GUIs etc so the thing is basically programmable.
The MAJOR problem that nobody thinks about is that all that graphically-driven, finger-touch stuff is very hard to work with in any kind of a safe manner WHILE DRIVING. Auto MFRs put a lot of time and thought into how radio head units are laid out so they're easy to use w/ just a few knobs, even having bumps on buttons and stuff so you can feel them w/o looking. The aftermarket radio folks don't seem to care as much, because they just need to sell units that look snazzy.
I bring all this up to point out that a complex fancy interactive thing in the hands of a young driver can be really dangerous.
I bought and put in a fancy head unit within 2 weeks of buying our Mazda5, and it didn't take longer before I realized how much I hated it b/c I had to stop driving to change music, which made it very tempting to try and do anyway. It's effectively the same as texting and driving.